Physiologists have long recognized that the hypothalamus controls all the secretory functions of the adenohypophysis with the hypothalamus producing special polypeptides which trigger the secretion of each pituitary hormone. A hypothalamic releasing factor has been characterized for the pituitary hormones thyrotropin and prolactin (the tripeptide TRF), for the pituitary gonadotropins luteinizing hormone and follicle stimulating hormone (the decapeptide LRF, LH-RH or GnRH) and for the pituitary hormones .beta.-endorphin and adrenocorticotropin (the 41-amino acid polypeptide CRF). An inhibitory factor has also been characterized in the form of somatostatin which inhibits the secretion of growth hormone (GH). Each of these hypothalamic releasing factors and somatostatin have been reproduced by total synthesis, and analogs of the native structures have been synthesized.
A corresponding hypothalamic releasing factor for the pituitary GH has long been sought after.